Magnetic tape reel

ABSTRACT

In magnetic tape reel having a cylindrical reel hub around which a magnetic tape is wound, and upper and lower flanges respectively extending radially outward from outer peripheries of upper and lower ends of the reel hub, when the reel hub and the lower flange are integrally molded of a magnetic resin material containing carbon fibers, a thickness t of a peripheral wall of the reel hub and a thickness t′ of the lower flange to be integrally molded with the reel hub are selected to satisfy the relationship given by 0.8t≦t′≦1.2t.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic tape reel formed of a synthetic resin material.

2. Description of the Related Art

Conventionally, as magnetic tape cartridges that are used as storage media for an external storage unit of computers and the like, there have been known those having a cartridge case which rotatably houses a single reel with a magnetic tape being wound around the reel.

As described, for example, in Japanese Unexamined Patent Publication No. 2002-352551, magnetic tape cartridges of this type generally have a single reel which is housed in a cartridge case in a rotatable manner. This single reel comprises a resin reel hub around which a magnetic tape is wound, and upper and lower flanges respectively extending radially outward from the outer peripheries of the upper and lower ends of the reel hub.

In this case, the reel hub and the lower flange are typically integrally molded of a synthetic resin material. The upper flange, which is also formed of the same or another synthetic resin material, is fixed to the reel hub by ultrasonic welding with the upper flange being fitted to a top end of the reel hub.

With the recent tendency of increasing data storage capacity, longer magnetic tapes have come to be used, thereby increasing a tightening force of magnetic tapes and hence deforming reel hubs. However, this results in contact between reel flanges and magnetic tapes and hence poses a problem that tape edges of the magnetic tapes are damaged.

In order to prevent the deformation of the reel hub, enhancement of the strength of the reel hub by incorporating fillers like carbon fibers into the synthetic resin material of which the reel hub is formed, has been proposed. Not only from a viewpoint of enhancing the strength of the reel, but also from a viewpoint of preventing the electrification on the reel surface, a carbon fiber is desirable filler.

However, the thermal conductivity of a polycarbonate resin and the thermal conductivity of a resin material which is a polycarbonate resin containing 10% of glass fibers are respectively 0.2 W/(m·K) and 0.23 W/(m·K), whereas the thermal conductivity of a resin material which is a polycarbonate resin containing 10% of carbon fibers is 0.45 W/(m·K), or as much as approximately twice those of the polycarbonate resin and the resin material containing 10% of glass fibers. Thus, the curing time during molding is relatively short, whereby the resin material becomes difficult to flow to a cavity portion located far from a gate of a molding die.

Meanwhile, the thickness of the flange of reel is typically as low as half the thickness of the peripheral wall of the reel hub, and the radially outer end of the flange is remote from the gate of the molding die. Accordingly, when a resin material in which carbon fibers are incorporated is used, the difficulty of flowing of the resin material to the radially outer end of the flange causes a larger deviation in height at the radially outer end of the flange from a reference level. Further, a difference in fluidity caused between the flange portion and the reel hub portion brings a new problem that controlling of the molding conditions is difficult.

In view of the foregoing, an object of the present invention is to reduce the aforementioned difference in fluidity during molding when the resin material in which carbon fibers are incorporated is used to enhance the strength of the reel, and hence to facilitate the controlling of the molding conditions.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a magnetic tape reel comprising a cylindrical reel hub around which a magnetic tape is wound; and upper and lower flanges respectively extending radially outward from outer peripheries of upper and lower ends of the reel hub, wherein when the reel hub and one of the upper and lower flanges are integrally molded of a synthetic resin material containing carbon fibers, a thickness t of a peripheral wall of the reel hub and a thickness t′ of one of the flanges to be integrally molded with the reel hub are selected to satisfy the relationship given by 0.8t≦t′≦1.2t.

More preferably, the thickness t of the peripheral wall of the reel hub and the thickness t′ of one of the flanges are selected to satisfy the relationship given by 0.8t≦t′≦1t. The aforementioned synthetic resin material is preferably a polycarbonate resin containing at least 5% of carbonate fibers.

In this way, when the reel hub and one of the upper and lower flanges are integrally molded of a synthetic resin material (for example, a polycarbonate resin) containing carbon fibers, a greater thickness t′ of the flange results in better fluidity. However, increasing the thickness t′ of the flange and hence reducing the ratio t/t′ of the thickness t of the peripheral wall of the reel hub to the thickness t′ results in deterioration of the cylindricity of the reel hub although the deviation in height at the radially outer end of the flange from the reference level during molding is reduced. In contrast, increasing the thickness t of the peripheral wall of the reel hub and hence increasing the ratio t/t′ results in increasing of the deviation in height at the radially outer end of the flange from the reference level although the cylindricity of the hub is improved and the strength of the reel hub is enhanced.

According to the present invention, the thickness t′ of the flange which is integrally molded with the reel hub is selected to fall within ±20% of the thickness t of the peripheral wall of the reel hub, whereby the controlling of the molding conditions is facilitated, and it becomes possible to reduce the deviation in height at the radially outer end of the flange from the reference level while maintaining appropriate cylindricity and strength of the reel hub.

Since a flowing distance of the resin material to the flange is longer than that to the reel hub during molding, it is preferred that the relationship t≦t′ is satisfied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE shows a longitudinal sectional view of a magnetic tape reel according to one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawing. FIGURE is a longitudinal sectional view of an inventive reel to be incorporated in a magnetic tape cartridge.

Referring to FIGURE, a reel 1 to be rotatably housed within a case of a magnetic tape cartridge (not shown) comprises: a reel hub 2 which is shaped in the form of a tubular member with an outer diameter of about 40 mm, a closed bottom and an open top, and around which a magnetic tape is wound; and lower and upper flanges 3 and 4 respectively extending radially outward from the outer peripheries of the upper and lower ends of the reel hub 2. The reel hub 2 and the lower flange 3 are integrally molded of a synthetic resin material. The upper flange 4, which is also formed of a synthetic resin material, is affixed to the reel hub 2 by ultrasonic welding with the upper flange 4 being fitted to the top end of the reel hub 2. For example, the reel hub 2 and the lower flange 3 may be integrally formed of a material which is a polycarbonate resin containing 10% of carbon fibers, while the upper flange 4 may be formed of only a polycarbonate resin.

The lower portion of the reel hub 2 is closed by a bottom wall 2 a, and a crown gear type reel gear 5, which is meshable with a driving gear (not shown) of a rotary driving member in a drive device (hereinafter referred to as the drive-side rotary driving member), is provided in an annular form at an outer peripheral portion of a lower surface of the bottom wall 2 a. Further, a metal plate 6 is attached to the lower surface of the bottom wall 2 a of the reel hub 2 within the reel gear 5 by insert molding. The metal plate 6 is provided because the metal plate 6 is magnetically attracted with respect to the drive-side rotary driving member, thus keeping the meshed state between the reel gear 5 and the driving gear.

A plurality of interlocking protrusions 7, each having a lock tooth 7 a at its extremity, are formed integrally with the reel hub 2 on the upper surface of the bottom wall 2 a so as to be circumferentially disposed at equal spaces from one another. When the magnetic tape cartridge is in the non-operating state, a locking member (not shown) having lock teeth, which are to be brought into mesh with lock teeth 7 a, serves to block the rotation of the reel 1.

In such an arrangement, the thickness t of the peripheral wall of the reel hub 2 and the thickness t′ of the lower flange which is integrally molded with the reel hub 2 are selected such that thickness t′ falls within ±20% of the thickness t. That is, the thickness t and the thickness t′ are selected to satisfy the relationship given by 0.8t≦t′≦1.2t.

In addition, since a flowing distance of the resin material to the lower flange 3 during molding is longer than that to the reel hub 2, it is more preferable that the thickness t′ of the lower flange 3 is selected to be greater than the thickness t of the peripheral wall of the reel hub 2 such that the relationship 0.8t≦t′≦1t is satisfied.

As is apparent from the above description, according to the embodiment of the invention, the thickness t of the peripheral wall of the reel hub 2 and the thickness t′ of the lower flange 3 are selected to satisfy the relationship described above. Therefore, a difference in fluidity during molding is reduced, forming of the reel is facilitated, and it becomes possible to reduce the deviation in height at the radially outer end of the lower flange 3 from the reference level while maintaining appropriate cylindricity and strength of the reel hub 2. 

1. A magnetic tape reel comprising: a cylindrical reel hub around which a magnetic tape is wound; and upper and lower flanges respectively extending radially outward from outer peripheries of upper and lower ends of the reel hub, wherein when the reel hub and one of the upper and lower flanges are integrally molded of a magnetic resin material containing carbon fibers, a thickness t of a peripheral wall of the reel hub and a thickness t′ of one of the flanges to be integrally molded with the reel hub are selected to satisfy the relationship given by 0.8t≦t′≦1.2t.
 2. The magnetic tape reel according to claim 1, wherein the thickness t and the thickness t′ are selected to satisfy the relationship given by 0.8t≦t′≦1t.
 3. The magnetic tape reel according to claim 1, wherein the synthetic resin material is essentially consisting of a polycarbonate resin containing at least 5% of carbonate fibers.
 4. The magnetic tape reel according to claim 2, wherein the synthetic resin material is essentially consisting of a polycarbonate resin containing at least 5% of carbonate fibers. 